It turns out there are many instances where interacting parties don't have a good way to share transactional data. There's no actual technical reason they don't, they just don't (think...banks FTPing files containing EBCIDIC encoded emulated punches card records to each other+). For these cases, blockchains that are managed (PoA) look like a pretty great solution.

+I've no idea if this actually happens, just trying to paint a general picture of crazy band aid stuff that happens.